[52.09] An Update on Timing the Geminga Pulsar with the EGRET Gamma-Ray Telescope

A 1998 observation of the Geminga Pulsar with the EGRET
gamma-ray telescope indicated a rotation phase which was
inconsistent with our 1997 ephemeris (Mattox et al. 1998).
The gamma-ray peaks were observed in July 1998 to arrive
0.15 +/- 0.01 of a rotation earlier than predicted by the
cubic ephemeris of Mattox et al. 1998. This suggests that a
glitch may have occurred for this pulsar. We will report on
an EGRET observation scheduled for May 1999 which will allow
us to search for a change in period derivative corresponding
to this possible glitch. The rotation phase measured in 1998
is not consistent with the possible sinusoidal modulation
reported by Mattox et al. 1998, and this deviation suggests
that the modulation apparent in 1997 is most simply
explained as timing noise. Current information is available
at http://gamma.bu.edu/~mattox/geminga.html.